1. Field of the Invention
The present invention relates to a piezoelectric vibrating piece, a piezoelectric vibrator, an oscillator, an electronic apparatus, and a radio timepiece.
2. Description of the Related Art
For example, in a mobile phone or a portable information device, in many cases, a piezoelectric vibrator is used which uses crystal or the like as a time source, a timing source such as a control signal, a reference signal source or the like. As the piezoelectric vibrator of this kind, there is a vibrator in which a tuning fork-like piezoelectric vibrating piece is hermetically sealed in a package formed with a cavity.
The package has a structure which causes a concave portion to function as a cavity by superimposing a pair of glass substrates in the state of forming a concave portion in one of the pair of glass substrates and directly bonding both of them. Furthermore, the piezoelectric vibrating piece includes a pair of vibration arm portions which is extended in a longitudinal direction and is placed in a width direction in a row, and a base portion which connects proximal end sides of the both vibration arm portions to each other, and the piezoelectric vibrating piece is configured so that both of the vibration arm portions are vibrated (oscillated) in a direction approaching and being separated from each other at a predetermined resonant frequency by using the proximal end side thereof as a starting point.
As a frequency adjusting method of the vibration arm portion of the case of manufacturing the piezoelectric vibrator configured in this manner, there is a method of adjusting the frequency of the vibration arm portion so as to become an object frequency by forming a weight metal film formed of Cr, Au, Ag or the like at the tip of the vibration arm portion in the piezoelectric vibrating piece in advance and partially removing (trimming) the weight metal film by the laser irradiation (for example, see JP-A-2002-164759).
However, in the piezoelectric vibrator mentioned above, along with a reduction in size of a mobile phone or a portable information terminal device, a further reduction in size and thickness is preferable. For that reason, a clearance between the piezoelectric vibrating piece and an inner surface of the package in the thickness direction is very narrow (for example, about 20 μm to 100 μm).
In this case, during an impact property test or the like which is performed by dropping the piezoelectric vibrator after the hermetical sealing, there is a concern that the vibration arm portion is vibrated in the thickness direction, whereby the tip portion of the vibration arm portion comes into contact with the inner surface of the package. Then, there is a problem in that the weight metal film formed at the tip portion of the vibration arm portion is peeled off by the impact of the time when the vibration arm portion comes into contact with the inner surface of the package, whereby the frequency of the vibration arm portion fluctuates.
In contrast, it is also considered that the weight metal film at the tip portion of the vibration arm portion is positively removed by the laser irradiation, but many weight metal films remain at the tip portion due to a position accuracy (for example, about 20 to 50 μm) of the laser irradiation.
Thus, the present invention was made in view of the problems mentioned above, and an object thereof is to provide a piezoelectric vibrating piece that is able to suppress the peeling of the weight metal film and suppress a fluctuation in frequency, a piezoelectric vibrator, an oscillator, an electronic apparatus, and a radio timepiece.